Sec Form 3 Filing - Breakthrough Energy Ventures, LLC @ ESS Tech, Inc. - 2021-10-08

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Breakthrough Energy Ventures, LLC 2. Issuer Name and Ticker or Trading Symbol ESS Tech, Inc. [ GWH] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O BREAKTHROUGH ENERGY INVESTMENTS LLC, 250 SUMMER STREET, 4TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 10/08/2021 (Street) BOSTON, MA02210 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock, $0.0001 par value per share 16,037,874 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Breakthrough Energy Ventures, LLC C/O BREAKTHROUGH ENERGY INVESTMENTS LLC 250 SUMMER STREET, 4TH FLOO R BOSTON, MA02210 X BREAKTHROUGH ENERGY INVESTMENTS LLC 250 SUMMER STREET, 4TH FLOOR BOSTON, MA02210 X Signatures BREAKTHROUGH ENERGY VENTURES, LLC By: BREAKTHROUGH ENERGY INVESTMENTS, LLC, its manager By: /s/ Christian Garcia Name: Christian Garcia Title: Authorized Signatory 10/18/2021 Signature of Reporting Person Date BREAKTHROUGH ENERGY INVESTMENTS, LLC By: /s/ Christian Garcia Name: Christian Garcia Title: Authorized Signatory 10/18/2021 Signature of Reporting Person Date

Explanation of Responses:

Remarks: The shares of Common Stock, par value $0.0001 per share, of ESS Tech, Inc. are held directly by Breakthrough Energy Ventures, LLC. Breakthrough Energy Investments, LLC serves as manager of Breakthrough Energy Ventures, LLC. By reason of such relationship, Breakthrough Energy Investments, LLC may be deemed to share voting and dispositive power over the Common Stock listed as beneficially owned by Breakthrough Energy Ventures, LLC. Breakthrough Energy Investments, LLC disclaims beneficial ownership of all such shares, except to the extent of its pecuniary interest.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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